A thermosensitive recording medium is used as a label for displaying an article name and an article destination. The thermosensitive recording medium has the property to make colorization in accordance with temperature. For example, on a plastic container used in a factory is affixed a destination (a delivery destination) of the article in a container and a label describing thereon an article name. The thermosensitive recording medium may be used in this label to write a letter and a symbol using a thermal head, etc.
Moreover, the thermo sensitive recording media include those of a rewritable type in which a colorized part may be decolorized by controlling the temperature of the thermal head to a suitable value. For the thermo sensitive recording medium of the rewritable type, the user may perform writing onto and erasure from a label affixed to the container, so that the operability may improve.
FIG. 1 is an exemplary drawing illustrating an exemplary drawing onto a thermo sensitive recording medium used as a label. In this thermo sensitive recording medium 14 are drawn multiple numbers, letters, figures, barcodes, etc. In order to be able to handle complicated letters, etc., when drawing a letter, etc., laser lights are collected by a lens to turn into a spot light. Therefore, for the laser writing device which irradiates the laser to draw on the label when drawing the letter, etc., with the laser, an irradiation position of the laser is controlled such that a stroke such as the letter, etc., is traced with the laser spot light.
FIGS. 2A and 2B are examples of a drawing which explains an exemplary drawing of a letter of “T”, which is drawn onto the thermo sensitive recording medium 14. FIG. 2A is an exemplary drawing of a printing apparatus such as a printer illustrated for comparison. “T” is formed by two strokes of a horizontal line and a vertical line. When drawing “T”, the laser writing device traces the two strokes with the laser spot light.
FIG. 2B is a drawing illustrating an example of sets of a starting point and an ending point of a stroke (s1, e1), (s2, e2). The laser writing device adjusts the position of the spot light with a galvano mirror, for example, to move the irradiation position to sl without irradiating the laser. Next, the irradiation of the laser is started (may be described merely as “laser ON” below) to move the spot light from s1 to e1.
Next, the laser writing device stops the irradiation of the laser (may be described merely as “laser OFF” below) to move the irradiation position to s2 without irradiating the laser. Next, the irradiation of the laser is started to cause the spot light to be moved from s2 to e2. In this way, two strokes are drawn and the letter of “T” is drawn onto the thermosensitive recording medium 14.
In this way, when the intended letter, etc., is formed onto the thermo sensitive recording medium 14, the laser writing device performs control with a command such as “turn the laser ON from a certain position to another position to move the spot light”. (a) in FIG. 3 is an example of a letter and a figure to be drawn, while (b) in FIG. 3 is an example of a scan instruction used by the laser writing device. The scan instruction means the content below in order from the left.    ln: line number (stroke number)    W: ON/OFF of laser (“1” is ON and “0” is OFF)    Sp: Coordinates of starting point    Ep: Coordinates of ending point    Pw: Output of the laser    Ve: scan speed
For the coordinates, what specifies the lateral position is handled as X, what specifies the vertical position is handled as Y, and the coordinates are shown as (X,Y). X increases in value when the position is closer to the right, while Y increases in value when the position is closer to the top. How the coordinate point is taken is one example. An example of the scan instruction is not limited to what is shown in FIG. 3.
Such a laser writing device may be used for forming an article name or a destination of an article for conveying the articles to sort the conveyed articles in a factory, distribution center, etc., so that it may be used in forming the article name, and the destination of the article. More specifically, the thermo sensitive recording medium 14 is pasted to the container which is successively conveyed by the conveyor within the factory, so that writing of the destination or the article name is performed with a laser on the individual thermo sensitive recording medium 14.
Here, the content drawn to the thermo sensitive recording medium 14 may always be fixed for an arbitrary period, or may be replaced for each writing target. The content to be drawn is often managed and controlled by an image processing apparatus which communicates with the laser writing device via an Ethernet card (registered trademark), RS-232C, etc. The image processing apparatus is configured with a PC (Personal Computer), for example. Moreover, the laser writing device itself can also manage the drawing content.
Here, as the manufacturer and the user of the laser writing device, the life of the laser writing device may be estimated. This is because, when the writing is continued even when the life has elapsed, failures such as the article name, etc., not accurately drawn could occur.
Thus, a method is devised of calculating life of a galvano mirror mounted on a laser processing apparatus for a user, etc., to grasp the time of replacing the galvano mirror (see Patent document 1, for example). Patent document 1 discloses a laser processing apparatus which calculates the period up to reaching end of life from the number of turns, or the operating time of a galvano mirror with a sensor installed on the galvano mirror.
However, in the laser writing device, a component having a life other than the galvano mirror is used. For example, in order to perform scanning with a laser light to efficiently heat the thermosensitive recording medium 14, the laser writing device needs to adjust the focal length such that the focal point of the laser light irradiated from the light source matches the writing position of the thermo sensitive recording medium 14.
FIG. 4 is one example of a drawing which describes adjustment of a focal length. In FIG. 4, a laser light is irradiated via a focal length adjustment unit 26 for a center vicinity P1 of the thermo sensitive recording medium 14 and an end part P2 of the thermo sensitive recording medium 14.
In order to efficiently heat the thermosensitive recording medium 14 with the laser light, it is preferable for the focal length adjustment unit 26 to adjust the focal point of the laser light to be in the vicinity of the drawing face of the thermo sensitive recording medium 14. The distance from the light source (FIG. 4 shows the distance from the focal length adjustment unit 26 for convenience) largely differs between the distance r1 in the center vicinity P1 and the distance r2 in the end part P2. In this way, the focal length adjustment unit 26 may optimally maintain the focal length when heating at positions whose distances from the light source differs.
Now, the focal length adjustment unit 26 is consumed (worn out) by operating repeatedly, so that it is preferable for a user or a manufacturer to replace it, before the focal distance adjustment unit 26 fails, with a new one, in order to normally form an article name, etc., in the laser writing device. Therefore, a method of estimating life of the focal distance adjustment unit 26 which can grasp the replacement time of the focal distance adjustment unit 26 is desired.
On this point, Patent document 1 does not disclose a technique of estimating a life of a focal length adjustment unit. Moreover, there is a problem that, when an angular sensor, etc., is installed in a focal length adjustment unit, not in a galvano mirror, the reversed times and the operation time are measured with the installed angular sensor, so that how long will be the life of the focal length adjustment unit may not be estimated unless the laser processing apparatus actually operates. Furthermore, as a problem associated with the fact that the angular sensor is installed in the focal length adjustment unit, there are also possibilities which lead to reduction in performance, such as the prolonged drawing time of the laser light irradiation apparatus.